1. Field of the Invention
This invention relates to an ultrasonic vibration treatment apparatus for effecting a treatment of a living structure, for instance such medical treatment as removal of a hypertrophic prostate or destruction of a calculus, by utilizing ultrasonic vibrations.
2. Description of the related art
Ultrasonic vibration treatment apparatuses, in which a treatment device for removing or destructing a diseased portion of the man's body, e.g., a hypertrophic prostate or a calculus, by utilizing ultrasonic vibrations is assembled in an endoscope, are well known in the art and in practical use. Such a treatment apparatus comprises a ultrasonic vibrator and a probe, e.g., a metal pipe, as a treatment device coupled to the vibrator for transmitting ultrasonic vibrations therefrom. In operation, the distal end of the probe undergoing ultrasonic vibrations with the operation of the vibrator, is directly urged against the diseased portion of the body for the removal or destruction of that portion.
In the prior art ultrasonic vibration treatment apparatus of the above construction, however, the amplitude of vibrations produced in the probe is greatly different at the time of actual driving, in which the distal end of the probe is held urged against the diseased portion for removal or destruction thereof, and at the time of idling, in which the probe is vibrated with its distal end not urged against but spaced apart from the diseased portion. This is so because the resistance offered to the probe is different between the above two instances. At the time of idling, substantially no resistance is offered to the probe. Therefore, the probe is vibrated with a very large amplitude compared to the amplitude at the time of actual driving. In consequence, the repetitive stress produced in the probe is increased, thus leading to early wear of the probe due to metallic fatigue.
A piezoelectric vibrator drive circuit disclosed, for instance, in Japanese Patent Disclosure Sho 54-140,526 (West German Patent Specification No. 2,916,540), is provided with an aim of overcoming the drawback noted above. The disclosed circuit makes use of a contact relation which is found between the drive current caused through the vibrator and the vibration amplitude. The vibration amplitude of the treatment device is controlled by controlling the drive current through the vibrator to be constant. In this way, early wear of the device such as heat generation or destruction can be prevented. Means for electromagnetically detecting the amplitude of ultrasonic vibrations are disclosed in U.S. Pat. Specification No. 4,579,000 and U.S. Pat. Application Ser. No. 20,333 filed Feb. 27, 1987 by the present applicant. In the former means, a coil is formed such that it surrounds a projection of ion or like magnetic material provided on a vibrator. In this case, vibrations of the projection accompanying the vibrations of the vibrator are measured as a change in the coil current. In the latter means, a permanent magnet is provided on a vibratory portion, i.e., part of vibrator or treatment device, and a coil is formed such that it surrounds the permanent magnet. In this case, vibrations of the permanent magnet are detected as a change in the coil current for measuring the amplitude of vibrations.
By using the above means, it is possible to control the vibration amplitude by controlling the drive current according to the measurement of vibrations of the vibratory portion. In this method of electromagnetic measurement of the vibration amplitude, however, extra components such as a magnet which are undesired in view of the status of vibration are directly mounted on the vibrator or treatment device. Consequently, the weight and shape of the vibrator or treatment device are changed to change the resonant frequency or impedance characteristics. Further, the characteristics values of the vibrator usually are not fixed due to fluctuations in manufacture. This means that the same vibration amplitude can not be obtained by setting the same current, and the desired vibration amplitude can not be obtained unless a current value is set for each vibrator. In some cases, the setting of a current leads to unexpected destruction of the vibrator. At any rate, it is difficult to permit stable control of the vibration treatment device.